This invention relates to olefin polymers comprising fluoropolymer processing aid and a cationic polyalkoxylate catalyst neutralizer. Such polymers possess improved melt rheology properties, especially reduced requirement for use of an interfacial agent to produce acceptable performance under melt extrusion conditions.
Olefin polymers such as polyethylene and polypropylene are often produced by use of a transition metal polymerization catalyst thereby leaving small amounts of catalyst residues in the polymer. Such residues are typically deactivated or neutralized to reduce color body formation by homogeneously incorporating a small quantity of a neutralizing compound into the polymer. This is normally accomplished by mixing the additive with the polymer while in a molten state or a polymer stream exiting a polymerization reactor.
WO-93/55920 disclosed the use of cationic derivatives of poly(oxyalkylene) compounds for use as catalyst neutralizers for olefin polymers. Examples included alkali metal-, alkaline earth metal-, and ammonium-derivatives of poly(oxyalkylene) compounds, especially potassium alkoxylate salts of mixed poly(oxyalkylene) compounds. Preferred neutralizers had number average molecular weights from 1000 to 3000 amu. Other conventional catalyst neutralizers include the alkali metal- and alkaline earth-derivatives of long chain fatty acids, especially calcium stearate.
Processing additives (PA) are compositions added to olefin polymer formulations to provide improved processability and throughput in melt compounding or melt extrusion applications. The additives also result in reduced melt fracture and improved surface properties in film and fiber applications. Suitable PA compositions include fluorinated polymers, especially fluoroelastomers or amorphous fluorinated polymers that are flowable at normal extrusion temperatures. Examples include tetrafluoroethylene homopolymers and copolymers, copolymers of vinylidene fluoride and hexafluoropropene, and copolymers of either tetrafluoroethylene, vinylidene fluoride, or hexylfluoropropene with perfluoro(alkyl vinyl)ethers, propene, or 1- or 2-hydropentafluoropropene. Preferred fluoropolymer processing additives have fluorine to carbon ratios of at least 1:2, and preferably at least 1:1. Additional disclosure of suitable fluoropolymer processing additives is found in U.S. Pat. Nos. 6,599,982, 6,642,310, 4,740,341, 3,334,157, and 3,125,547, and elsewhere.
Combinations of fluoropolymer processing additives with additional components are known in the art. In U.S. Pat. Nos. 5,707,569, 5,587,429 and 4,855,360 combinations with an interfacial agent, such as a poly(oxyalkylene) polymer or an ionomer are disclosed. The PA may additionally include conditioners such as talc and/or calcium carbonate.
Disadvantageously, when conventional catalyst neutralizers, such as calcium stearate, are employed in olefin polymer formulations that additionally include a fluoropolymer containing PA, an undesired interaction with the interfacial agent, especially any poly(oxyalkylene) polymer or ionomer, may occur. This may result in a need to use increased quantities of interfacial agent in the PA composition, thereby increasing costs of the additive composition and leading to adverse affects on polymer performance or processability.
In the previously mentioned U.S. Pat. No. 5,707,569, use of a polar side-group containing extrusion adjuvant effective to counteract the deleterious effect of components such as calcium stearate or other divalent or trivalent metal ion containing compounds on the fluoropolymer/interfacial agent containing PA was disclosed. Suitable adjuvants included polar group containing polymers such as vinyl ester homopolymers, copolymers of an olefin and a vinyl ester, copolymers of an olefin and an α,β-unsaturated C3-8 carboxylic acid, and ionomeric derivatives thereof (col. 3, line 64-col. 4, line 11).
Accordingly, despite the advance in the art occasioned by polymer blends comprising conventional catalyst neutralizers and fluoropolymer containing PA compositions, further improvement in such polymer compositions is desired. In particular, formulations wherein a reduction in deleterious interference with interfacial agents occurs are still desired. In addition, the attainment of equivalent or improved polymer performance while utilizing reduced quantities of interfacial agent is desired.